The invention is directed to thermoplastic mixtures suitable for the production of synthetic resin films having antiblocking properties.
In the production of, e.g., flexible tube films from thermoplastic synthetic resins or synthetic resin mixtures a melt of these thermoplastic mixtures is extruded through a circular slot nozzle to form a flexible tube, this is blown, cooled, laid flat and wound up.
It is known in the production of films as a particularly important requirement to provide that there is prevented the blocking of the films.
Thus according to German AS No. 1 210 177 (UCC) (corresponding to Mock U.S. application Ser. No. 679,534, filed Aug. 21, 1957) now abandoned there is known a process for production of non-blocking, transparent polyethylene films in which a finely divided SiO.sub.2 containing material with a particle size of 0.5 to 7 microns is kneaded into the extruding mixture through which there can be prevented a blocking of the films.
According to this German AS No. 1 210 177, there can be added as SiO.sub.2 containing materials diatomaceous earth, commercial silica and silica gel whose particle size distribution lies within this range.
From Bollen U.S. Pat. No. 4,029,631, it is known to mix an amorphous silicon dioxide into polyethylene terephthalate as an antiblocking agent.
From German AS No. 1 232 337 (Kurashiki Rayon Co.) it is known in the production of film tapes from polyvinyl alcohol to dust on the surfaces of both film tapes a block preventing powder consisting of water free silica with a degree of purity of 99.9% and a particle size of 4 to 13 millimicrons.
From German AS No. 1 247 641 (UCC) (corresponding to Gardner U.S. application Ser. No. 333,206, filed Dec. 24, 1963) abandoned, it is known to Knead into thermoplastic mixtures for the production of films from polyethylene as fillers diatomaceous earth, commercial silica, silicates, silica gel, silica-alumina and asbestos.
However, the known thermoplastic mixtures have the disadvantage that they contain as antiblocking agent materials which must be made nearly free from water in expensive drying processes prior to their being kneaded into the thermoplastic mixture, since the presence of moisture in the thermoplastic mixture causes the formation of blisters or bubbles at the stated processing temperatures.
The problem of the present invention was to find a thermoplastic mixture with an inorganic filler which in a synthetic resin film exhibits a good anti-blocking effect and whose inorganic filler components do not need to be dried to a water free condition.